Distribution of the freshwater snail Gyraulus rossmaessleri (Auerswald, 1852) (Mollusca, Gastropoda, Planorbidae) at the present and past western limit of its range (north-eastern France)

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Gyraulus rossmaessleri (Auerswald, 1852) is a freshwater planorbid gastropod that occurs mainly in lowland temporary water bodies and is widespread in Europe as far as Siberia. Its presence in France has only been recorded in Alsace in the Upper Rhine Valley, which represents its westernmost distribution boundary. In this paper, we report and describe new localities from the Alsatian rieds, emblematic regional landscapes of flooded meadows. These new data significantly extend the regional distribution of G. rossmaessleri. The species seems to be restricted to damp or wet oligotrophic grasslands, especially with Molinia caerulea, hygromesophilic hay meadows at low and medium altitudes, hygrophilic hay meadows flooded for long periods by rising groundwater, meadows with water ragwort and marginal to marshy willow shrublands. Although these habitats may be more or less extensive and open, the species is only found in small patches in depressions and/or shaded areas. According to our observations, individuals can survive several months of drought in summer by withdrawing deep into their shell and closing it with an epiphragm. These key microhabitats appear to be essential for the maintenance of species in the floodplain meadows of the rieds, which are under pressure from intensive agriculture and recurrent droughts. In addition, our review of palaeontological data suggests that during the Middle and Late Pleistocene G. rossmaessleri was more widespread along its western margin and was associated with a cold-tolerant fauna. Finally, given the general decline of the species, the loss and pollution of habitats, particularly in the Upper Rhine Valley, and its remarkable ecology of both dry and cold-adapted species, we argue that Gyraulus rossmaessleri should be better considered in the management and conservation of natural areas and/or could play a key role as umbrella/flagship species for the conservation of these iconic regional habitats.